The invention relates in general to a liquid crystal display (LCD) and a driving method thereof, and more particularly to an LCD capable of suppressing cross talk, and a driving method thereof.
In the field of LCD technology, the quality of an image displayed on an LCD panel may be detrimentally affected by a cross-talk phenomenon that results from voltage offsets on the common electrode of a pixel. To illustrate the effects of the cross-talk phenomenon, consider FIG. 1A (Prior Art), which shows an example of an image to be displayed by a conventional LCD. FIGS. 1B and 1C (Prior Art) show the gray levels that should be displayed by the pixels in regions 10 and 20 of the image in FIG. 1A, respectively. FIG. 1D (Prior Art) shows an image that is actually displayed by the conventional LCD. As can be seen in FIG. 1D, the displayed gray levels in the regions 121 and 122 of the displayed image do not accurately correspond with the gray levels that should have been displayed. The poor quality of the displayed gray levels in FIG. 1D is due to the cross-talk phenomenon.
FIG. 2 (Prior Art) is a circuit diagram representing a pixel of an LCD. As shown in FIG. 2, the pixel includes a transistor 210, a storage capacitor Cst and a liquid crystal capacitor CLC. The transistor 210 has a first terminal coupled to a data line 240, and a second terminal coupled to each of the first terminals of the storage capacitor Cst and the liquid crystal capacitor CLC. Second terminals of the storage capacitor Cst and the liquid crystal capacitor CLC are respectively coupled to a common electrode 220 of a lower substrate and a common electrode 230 of an upper substrate (i.e., a transparent electrode (ITO)). A parasitic capacitor is formed between the data line and the common electrode, wherein a parasitic capacitor Cxd is formed between the data line 240 and the common electrode 220, while a parasitic capacitor Cxu is formed between a data line 250 and the common electrode 230. The formation of these parasitic capacitors contributes to the occurrence of the cross-talk phenomenon.
More specifically, when the data lines 240 and 250 experience voltage fluctuations, such as when the voltages at the first terminals of the parasitic capacitors Cxd and Cxu fluctuate, the levels of the voltages at the second terminals of the parasitic capacitors Cxd and Cxu (i.e., the levels of the common voltages at the common electrodes 220 and 210) fluctuate therewith. As a result, when the transistor 210 is turned on, the voltage stored on the storage capacitor Cst and the liquid crystal capacitor CLC is offset so that the gray level actually displayed by the pixel is different from the desired gray level. For instance, when the image of FIG. 1A is to be displayed, the LCD instead may produce the image of FIG. 1D. As shown in FIG. 1D, the regions 121 and 122 have different brightness levels and tones from those of the image in FIG. 1A so that the image quality is poor. This degradation in image quality is the result of the so-called cross-talk phenomenon.